Conventionally, there has been provided a lighting device that includes two or more lighting circuits connected in parallel with a single DC power supply (e.g., see JP 2013-109913 A). Each lighting circuit includes a capacitor that is connected between output ends (hereinafter, referred to as an “output capacitor”). The two or more lighting circuits are configured to light two or more different light sources, respectively. Each light source is constituted by a series circuit of two or more light-emitting diodes.
For example, when the lighting device includes three lighting circuits, and colors of light emitted from three light sources connected with the three lighting circuits correspond one-to-one to three primary colors of light, respectively, various light colors can be realized as the color mixture of the light from the three light sources, by the three lighting circuits being controlled individually.
Here generally, in a case where a light source includes a solid-state light-emitting element such as a light-emitting diode, the light source emits light when a voltage input to the light source is a prescribed forward voltage or more. In other words, when each of the above-mentioned lighting circuits starts operation for causing a corresponding light source to emit light, the corresponding light source starts light emission at a time when an output voltage of the lighting circuit (i.e., a voltage across the output capacitor thereof) reaches a forward voltage of the corresponding light source.
However, depending on a difference between forward voltages of the light sources or a difference between time constants of the circuits, there has been a possibility that a time period between a time point at which a lighting circuit starts operation for causing a corresponding light source to emit light and a time point at which the corresponding light source actually emits light (hereinafter, referred to as a “start time period”) may be different from that in the case of another lighting circuit.
Especially when brightness is adjusted by intermittent lighting, the difference between the start time periods causes variation in the brightness and further variation in the light color provided by the color mixture.